A sealing boot assembly comprises a flexible boot having a first end in sealing engagement with an outer surface of a shaft to define an inner chamber therein. A venting orifice extends from the inner chamber through the flexible boot to ambient and a moisture-blocking, vapor-breathable membrane is disposed across the venting orifice between the inner chamber and ambient to vent gas from the inner chamber during high temperature operation of the shaft and to allow air to returns to the inner chamber upon cooling thereof.